Method and apparatus for electric heating by high-frequency currents.



E. F. NOHTHRUP. I METHOD AND APPARATUS FOR ELECTHICHEATING BY HIGH FREQUENCY CURHENTS.

APPUCATIQN HLED SEPT. 19. 1911.

11,286,394. Patented Das. 3, 12H8.

2 SHEETS-SHEEI l.

Hum

VVVHH E. 5,. JORHRUP. A MTHOD MJD APPARATUS FOR ELECRIC HEATING BY HIGH FREQUENCY CURRENTS.

APPLICATION man SEPT4 19. 19H. 392%3944 Patented Dec. 3 1918.

` 2 suns-snaar 2.

vwefntoz EDWIN IF. NORTHRUP, 0F PRINCETON, NEW JERSEY,

COMPANY, 0F PHILADELPHIA, VANIA.

ASSIGNOR T0 THE AJAX METAL PENNSYLVANIA. A CORPORATION 0F PENNSYL- METHOD ANI) APPARATUS FOR ELECTRIC HEATING BY HIGH-FREQUENCYA CUBRENTS.

Speciilcation of Letters Patent.

Patented Dec. 3, 1918.

Application led September 19,1917. Serial No. 192,049.

To rt 1f/toni t may concern.'

Be it known that I, EDWIN F. NoRTHaUr, a citizen of the 4United States, residing at 30 Wigginastreet, Princeton, in. the county of Mercer and Siate of New Jersey, have invented a certain new and useful Method and Apparatus for Electric Heating by Highl `requency Currents, of which the followin` is a specification.

he primary purpose of my invention is to transfer' electric energy into a continuous mass by electromagnetic induction and' there to convert the electric energy into thermal energy in such mass by means of high frequency currents and without the whole or partial interlinkage of a ferro-magnetic with an electric circuit. The high fre uency cur, rents may be interi'nittently supp ied, being damped out proportionally to the rate of energy consumption or the high frequency current may be sustained by continuously supplying energy at a rate equal to the rate of energy consumption.

A further purpose of my invention is to take advantage of the enormous rate of change of high frequency currents ininduction furnace work to eliminate necessity for a whole or partial interlinkage of a ferro-magne'tic circuit with an electric circuit.

A further purpose of my invention is in a heating s stem, to heat masses for the uror preparing t em for work, by other processes, (all herein enerically referred to as electric furnaces) y means of the heating ,effect of electric currents having the natural -frequenc of an oscillating electric system, having elther damped or ma/ntained oscilla-- terchangeably for electric furnace operation either a resonant circuit havmfg maintained oscillations or the discharge o a condenser', the energy being impressed upon cu'cult them or heat-treating t ernv p in which the oscillations take place by different means such as for example, as by an alternating current generator with the frequency of which the oscillation current circuit is approximately in tune or by an altermating current generator merely charging the condenser as desired. y

A further urpose is to heat a resistor by circulation of) high fre uency currents within it through action o electric current induced as distinguished from h steresis and without necessity for iron inter inkage.

A further purpose is to make an electrically conducting but desirably not paramagnetic resistor which is to be acted upon the secondary of a primary comprisin oneor more inclosing or contlguous osc" ation coils and discharging a condenser ofcoudensers through this primary to induce currents of corresponding period within the resistor Without requiring interlinkage of iron to secure the transfer. p

A further purpose is to pass maintained free oscillations or current about a resistor in a heating system, secur continuous transferl of current, and thus o heat, to the resistor.

A further purpose is to approximately tune an'oscillating circuit for an electric furnace to a. high frequency alternating current slllpply circuit by which the energy is sup- A further purpose is to produce an electric furnace which takes a leading current, enabling me to use the lagging current, usually available, to advantage and to compensate by positive rcactance so as to secure 4unity power factor.

A further purpose, where a liquid or molten conducting ool forms the reslstor, is fn secure stirring y the same induced current that causes the heatin Further purposes will appear in the speci? I fication and in the claims hereof.

I have preferred to illustrate my invention chiefly diagrammatically, in view of the broad character of the invention, and have applied it to but one art and to but two illustrations in that art, amo arts and many forms in which 1t may be ctrthe various ried out,selecting therefor an art which is n important and forms which are ractical,

eiiicient and simple, in which my invention has high commercial utilit and which at the same time illustrates the principles of my invention to considerable advantage.

Figures l to 6 are diagrammatic views iilustrateive of my invention.

Fi s. 7 and 8 are da rammatic views showing in a more or less ypothetical way the directions of flow of induced currents of electricity and of a molten resistor when my invention is applied to furnace operation..A

Fig. 9 is a sectional view showing one application of my invention, there applying to a vacuum crucible furnace.

lx1-the drawings similar' numerals indicate like parts.

My invention as illustrated applies oscillatory electric currents to the heating of conductingy material. My invention resides both in the general application ot the principles involved and in the processes and apparatus by which these `principles are utilized in the particular art from which l have taken my illustration.

The, introduction of inductance into the circuit of an alternating current transmission line under forced vibration causes the 'current to lagI in phase behind the elec- /tromotive force, and capacity so introduced causes the current to lead in phase. The reponderance of induction over capacity oth in the line and in the coils ot existing induction apparatus applying heat has reduced the power factor making it prohibitively low in otherwise desirable installations. With a relatively small amount ot.

power available tor use. this low power factor requires an equipment in proportion to the relatively 'large currents flowing in the line and heat is developed where it is Vnot only not required but even injurious.

li, on the other hand, electric energy he applied to a circuit containing a condenser and the latter be then allowed to discharge itself through a closed circuit. the electricity oscillatfes back and forth like a pendulum.

lt the oscillations he damped proportionally"to the rate otdissipat'ion of energy. as would be the case when the condenser is charged and discharged through a gap withopt provision tor maintaining the amplitude. the oscillations reduce in amplitude until the energy stored in the condenser is .inally dissipated in electric radiation and in heat. ln this form the edectivc transfer of energy takes place intermittently. during a part only of the time. For each discharge and recharge, the discharge takes place durina' a part only of the total time. the time of recharge being relatively Wasted.

ere the circuit is a resonant one. (which may, nevertheless, contain a discharge gap) masas the oscillations are maintained, e'. e., are s also oscillate continuously, and energy transterence takes place throughout the entire time.

ln'the tirst (damped) form the inductance of the circuit does not adeot the total energy transformed, only the natural frequency, the time within which the oscillations will cease (the damping factor) and the number ot oscillations. ln the resonant circuit the inductance does not'aftect the total energy transformed but must be proortioned to the capacity of the other ranch so as to tune the circuit to the trequency of the alternating current. supply.

The inductance in the damped form is comparable with the mass of a ball swinging at the. free end of a spring whose opposite end is fixed. rlllnere is no dissipation of energy in thisV mass aud its increase merely alters the ,period of the vibration. thc time within Whichthc spring comes to rest and the number of vibrations of the spring. lli the ball he given sufficient nnpulse. throughout each oscillation to inanitain the same amplitude, so that the spring does not come to rest and the oscillations become continuous. this comparison applies to the resonant circuit having maintained oscillations.

lf thc capacity and inductance be large. the fraction ot energy dissipated in radiation is negligibly small. The movement of electricity in the circuit constitutes a nar-ural. untorcedor free vibration having a period l T 21a-@ where C is the capacity and L the inductance of the circuit.

induetance y placing the condenser-s in multiple 'or splitting up the oscillation coil.

into parts fed from different condensers, which may be placed in multiple, by special non-inductive line construction and in other `trays.'

ln the illustration having sustained oscillations and a resonant circuit the period becomes the same or nearly that of the altermating current supply and the tuning or. the circuit is, ot cdurse, dependent upon this agreement.

lt might he noted that'the currents in an oscillation resistor subjected to the induence of .the impulses correspond to those in the Sillil@

total values of capacity and l Oscillation con in period and foiiow the fluctuations of the oscillatory currents even n are where there is ohmic resistance or where there is an inductively coupled circuit hai ing ohmic resistance, such as a solid. liquid or plastic body of conducting material or container or holder therefor forming a Secondary to such a free oscillation primary.

The oscillation circuit can be transmitted a considerable distance from the location of the Condensers with low heat losses and converted at the distant point almost wholly into heat. The conversion will comprise an integration of the impulses in the osciliation resistor corresponding; to the oscillatniii or oscillations in the indiictor coil.

As the .energy stored in the condenser is one half its capacity times the square of the voltage to which it is charged, the sole dctermining factors for the available energy from a single char e are thev size of the condenser and the voage a plied in charging it. The power is then determined by the number of times the condenser is char ed to tliisvoltage and discharged per unit o time.

The inductance of the circuit, the resistivity of the metal constituting the secondary coupled circuit or resistor and the i closeness of the coupling have no eiect upon ,the power generated and, theoretically, no e'ect upon the power delivered to the resistor. v

Discussing nw the first form, having damped oscillations Where the available voltage is sullicient to charge the condenser directly from it, no transformer is required between the sup 1y and the condenser and I have shown sucii a. construction in Fig. 1. The theory will be well understood from this ligure. A single phase alternating current circuit is shown having sides A, A. The condenser to be charged is shown at C, the oscillation coil, through which the condenser discharI es, at

0, the inductance of the two sides of t e circuit at L1, and L2, L4 and a discharge gap at G. -These inductances are mtended to represent thc entire inductance of each side of the circuit and are divided for convenA ience in the later discussion.

The energy stored at each char CV. When the discharge gap breaks down, the ener will surge in the oscillation circuit until it is all dissipated rin radiation and heat, for low frequencies almost entirely in heat.A

The means of dissipation are as follows:

1Dielectric loss in condenser.'

2-IR loss in dischar ga G.

3--IR1 loss in line, w ere l is the ohmic cycles and 12,500 cycles resistance of the line possessing nductanoe an L1-12R2 10m where R is the ohmic resistance or its equivalent of that portion of circuit where it is desired to convert the en- -crgy 1/2 CV2 into heat.

-Radiation loss. This is the radiation of energy utilizedy in radio telegraphy and is quite ne ligible for low frequencies and especially or non-linear, non-open circuits here used.

-Losses in the l'transformer D which feeds the oscillatory circuit.

f It is indifferent whether R is a resist ance located' in the oscillatory circuit or whether it is a resistance in an inductively coupled circuit, i. e., in the oscillation resister, or the sum of these; and because the secondary circuit constitutes but a single turn within the mass and the inducing circuit lias several turns, the magnitude of the current -in the oscillation resistor is corre spondingl eat.

In speablritiilg of the massf I desire to make clear that, though in some uses of my invention the oscillation coil may operate upon a thick mass, such as -a billet, bloom or other unit of metal to be worked, the shape may vary widely accordingl to the applica'- tion intended and vmay be, lfor example, a mere shell of cylindrical or other shape, the resistor being permissibly solid, in paste form, molten or normally liquid.

The oscillation coil 0 in the illustration happens to form apart of two circuits. It is part of the alternating circuit for charging of the condenser and also constitutes an oscillation prima in the discharging circuit for the oscilation resistor as a secondary.

In the eort to transmit the energy stored in otential form in the condenser to the con ucting material heated with maximum eiciency, it is indifferent, within wide limits, what may be 'the natural frequency of the oscillatory lcircuit. I have obtained substantially equal frequencies with 25,400

r second respec- The eiliciency whiisli we wishto get is Ese tively.

where heat in the oscillation resistor and P thi power su plied at the primary terminals of the trans ormer.

To obtain high efliciency the following losses must be small:

1Dielectric loss. (Low frequency of oscillation will contribute make thisV loss Smau? 2+ *R1 loss in disclia e gap. 3--IRl lo in line. o make this losesmall the ohmic p is power dissipated and held as e ency of the other means, such as blowing; out the- 'chargn EL, and L2 arelarg'e (which does not ect power) and their ,ohmic resistance 1s negligible they will not diminish the power transmitted in the oscillation circuit whileA the potential drop will take place chiey over them, so that the potential dro at the ends Since thesupplyoi alternating current will seldom agree in voltage with that deindicated diagranunatically sired to charge the. condenser, the circuit will more usually be as indicated in Fig. '2, where the supplycircuit A, A', is transformed at D and the v'condenser is charged from the secondary transformer connections c, 'While the vshort circuting of the supply, (here taking place in the secondary) across the discharge gap, can still becontrolled hy prary indnctance, or by special provisions for blowing or `vacuum at the discharge, it is more desirable to control it by inducta'ncc Vin that portion of the circuit between the discharge gap and the transformer secondary,

at. Z3, 4. The discussion ot Fig, l is then applicable to this orun also with the change in symbols from A, il', to a, a', and 'L es Les to. la: 14 In Figs. ll and 2 the oscillation coil may be placed in the discharge gap connection, #free from the charging circuit, it desired.

ll-have shown different resistors in the two the resistor W in Fig. l beiner the molten., or otherwise liquid electrically-conducting content oan electrically non-conailuetingg7 crucihle ll, whereas the resistor in. Fig. 2, shown at W2, is a bloom ori-billet et metal which is to ,he worked.

ln Figs. 3 and 4f ll have illustrated my inrention es' applied to. a multipliase circuit without' nnhalancing the phases, selecting two phase' for the illustration because it presents the simplest torniand, therefore the" torni capable et easiest clear explanation.

Because transformers wille be required usually to step-up the roltage from that a, a, we

arailahle to themuch higher rolmge under which my invention becomes most emcicnt, l have own transformers here, the system Mingpracticahle wherever two `phase current may he obtained. 'lhe transformers can he ottcd where the commercial current is et suitahle roltage.

' Flhe two hase primary circuit has sides E', connecting with the `primaries respectively ot transformers D, D'.,V The secondaries Aof these' transformers are shown as united at N., The other seconary incassa terminals and the neutral are connec 1 to opposite sides of respective condensers C, C', which arcarrangcd to discharge through any suitable discharge gaps G, G. lt'will be seen that the discharge circuits do not in-4 clude the. seconda ries ot the transformers.

.-'lt some suitable. point or points in the discharge circuit l place an oscillation coil or coils shown as (l, and 0. which form the heating coils for thefurnac'e or' (as shown in Fig. 3) for two furnaces and may surround a single resistor or, as shown, separate resistors which. ma v here, tor illustration, be either electrically conducting7 cruciblescll, il or their contents. W? it the latter he electrically conducting. 'lherc isy some advan tage iu placing coils within the separate circuits in the gure shown instead of using one coil within the neutral connection, in that the torni shown protects againstloss of effect-ive energy through discharge of the condensers and gaps in series, which discharge would not passthrough a heating coil placed within the neutral connection.

.ily furnace takes a leading current; z'. e., the secondaries of the transformers, or the primari" current supply where there are no transformers, leads into an initial negative. reactancc. illost commercial circuits have a. lagging current and my furnace can he connected with such a supply to @great advantage, adjusting by positive reactance 'to-balance the las of the supply current and thi` lead' of the tui-nace current and secure unltylpower factor. l hare illustrated connections for this m lg. l, where thecircuits are -intended to correspond generally with lfgr. 3. except that adustable positive reactances L L., are included in -theprirnary supply foi-,the purpose indicated. The coil windings in the two circuits are` shown as .surrounding the saule resistor W4; (which may be any species of the resistor W), and as continuous, with a tap atthe middle from the neutral connection. The adjustable reactanees could, et course, loc placed within the secondary windings instead et within the primary as shown.

The user can oftcn purchase power `more `cheaply tor supplying,P a 'load that has aninitial leading current.

ill@

lll@

l purposeusing alternating current supply nand l desire to he understood as includingr, .in this term such makeshitts or substitutes as charge condenser-s without actually using alternating currents', regarding these "substitutes as electrical equivalents ot the alternating current tor this purpose. Obviously current supply of therequir `potential could he connected directly lto the lines instead shown. g

`Where there is no resonance, and the condenser and harge gap aroused to provide ot through the transtoers `free oscillations, the frequency of the primary circuit is not of primal importance thoughsthe rate of discharge and the voltage of the current passing through the discharge circuit are important since they atleet both the number and the rate of succession of the im ulses.

n the use of multiphase sup ly it will be noted that the discharge from iiferent condensers is likel to occur at different times since they are charged by currents of diiercnt phase. In operation the y'multiphase electromotive forces are impressed on the primaries of the two transformers and the condensers are charged to a break down potential with the discharge gap adjustment used. As each discharge gap breaks down the oscillato current surges through the oscillation coll or coils which, acting as a primary will induce oppositely dlrected current dow in resistor W, forming the oscillation secondary. The secondary dow is in substantially parallel lanes or strata to that in the inducing oscil ation coil.

lW ith the very great rate of change of current flow, secured by high frequency, due to therapidity ot the reversals, the electric impulses transmitted to the resistor are -very large without the necessity for interlinking any magnetic circuit with the resistor circuit. I believe that l am the rst to produce eective electric heatin by induction without the interlinkage org a magnetic circuit, by which I mean a ferro-magnetic circuit, and that Iam also the tirst te benelicially apply high frequency currents of any character to the electric heating art. lt will be noted that my invention does not depend upon the hysteresis of magnetizable material nor upon the use of 'a magnetically permeable core, casing or resistor, but requires only that the material to be acted upon or an ancillary mass or container in suitable heat-transferring relation to it shall be a conductor of electricity.

The successive chargin of the condensers will alternate, as will also' their discharges, at intervals depending upon the capacity of the condensers, the applied voltage and the extent of separation ofthe diacharge gap, resulting in a rapid series oi heating electric impulses within the 'resistor which, when applied to a liquid or molten resistor tend to stir the resistor. The current density in the metal 'may be made eat enough to produce eiective stirring.

he stirring and the rate of heating are both proportionate to the rate of energy inputin a given volume of resistor.

The rateof input is of course dependent upon the number ofalternations. In my own operation 'of -the invention I have used thousands of alternations per `second with great success.

In order that the broad character of my tion, which differs rom the first in that the furnace circuit is tuned to the extent that the supply current is nearly in phase with its voltage in agreement with a high irequency'and preferably high voltage supply, so arranged as to secure the advantage of condenser action without the necessity for discharge gap use though permitting discharge gaps to be inserted if desired. By this arrangement I secure an uninterrupted series of oscillations, each of full amplitude.

lt is my purpose to include in this application claims covering broadly the application of high frequency currents to electric heating; and to the transfer of electric energy for 'conversion into heat Within a resistor through electromagnetic induction and without need of partial or complete interlinlting of transformer iron or-'li te paramagnetic material'vvith an electric circuit to effect the conversion; as well as upon oscillation current discharge through a coil for heating purposes, talting claims for that purpose from my copending application, Serial No. 133,474 for oscillation current method` and apparatus. led November 25, i916. ll plan toclaim specifically in that ease subject matter which is not claimed in this application and to claim Within this present application in addition to the broad subject matter indicated, the form hereinafter described using a resonant circuit.

It is my purpose to transfer also to thisI application, claims now pending in my application for oscillation` spiral coils and connections filed June 18, 1917, Serial No; 175,519, upon subject matter relating to the provision of a furnace circuit taking a .leading current, or having a negative reacjt anlce,.and the supplying of positive react-ance whereby unlty power factor may be obtained when my circuit is connected with 'supply circuits having the usual lagging current.

.In the .second form of my invention, illustrated diagrammatically in' Fig. 5 and by vector diagram in Fig, 6, I supply 'current from any suitable alternating current source of supply shown'as an alternating currentdynamo which preferably gives high voltage dire'ztly or through the medium of av transformer and at high frequency and requires but a small supply current for the power furnished. I applv the current at points p p upon opposite sides of a condenser C2, herevshown to be ad3ustable, in a. circuit exactly or approximately tuned vto the frequency of the generator circuit and containing the condenser in one branch and an inductance L, in the other. The inherent resistance of the two circuits l have represented as r and R respectively. The current in the generator circuit is represented as I, that in the branches as I; and Il, the electromotive forces in the enerat-or circuit and in the several .parts o the inductance circuit as F., E, and Ex and the equivalent resistance of the part of the circuit at L, as X1, respectively.

The inductance coil ,L7 is a furnace coill and may be made to operate upon any resistor as freely'as any of 4my other furnace coils. With the connectionsshown, relatively large currents How Within the condenser and inductor coil (furnace) circuits.

The currentfvalues in such a circuit'h'avn ing assignedronstants and without 'tuning have been indicated in an example given in Bedcll & Crehore on Alte'matz'ng Uma-ents, :1rd edition on pages 308-310, showing the currents in the two branches to be Greatly in cncess of the current in the suppy circuit.

It will be recognized that ithe currents therein are out of phase with the voltage of the supply, one 'leading the electromotive force and the other lagging behind it.

No discharge gap is required and the advantage from one is at least questionable. Obviously one could' be inserted,.it` otherwise desirable, without rendering the apparatus or method inoperative. Any assigned advantage from -an intendedv discharge gap would merely be compared with' its inherent energy loss to determine the advisability of linserting it. l

Taking up the vector diagram, Fig. 6:- Because the resistance '1' is negligible the current Ic may be plotted ninety degrees` in advance of the electromotive force and its value m'ay be fairly considered Ic=E2 NC.

The resistance and current in the inductive branch `(or the equivalent inductive coupling of the resistor vheated by the coil) determines thezvalue of the E.. M. F. cum-N ponent E, which lags behind the electromotive force nearly ninety degrees. The value -of the current 'Il is givenI by the followin relations; this current being in phase with a. M. F. .component and behind the E. M. F. component E..

electromotive force 1s Psaum/Tf assesse- A condition of :we :una in the circuit is preferable to exact tuning, as. true resonance would cause the current I to slightly lead the clectromotive force E as distinguished from exact phase relation as illustrated in this diagram, not a serious diference. l llFroim the equation Parri-.2 it will be seen that a high clectromotive force may be used to great advantage here since the supply current may be reduced fto very small values. Il and L may closely approximate each other in value.

Again since the value of E, is plotted as a chord within a circle having diameter E it can be seen from the vector --diagram coil; showing that as inductive coupling between the coil and the resistor increases, and consequent increased work is done, the dynamo will he called upon to supply correspondingly more power.

()ne advantageous use of high electromotive torce and low currentvalues is to accommodate. this method to inexpensive dynamo construction and low transmission losses where the current is transmitted'any considerable distances.

As a result of theapproxiniate tuning to the frequency ofthe. supply circuitthe oscillations 4from the condenser discharge are continuously accelerated in proportion to the drag. retardation or damping to which they are subject during their oscillation be- `cause of the transfer of the energy to thev resistor, so that the full maximum amplitude and strength of these oscillations is mintainedas distinguished from the rapid y' reducingamplitude and strength of the damped oscillations used by me in my method described in connection with 1-3.'

Since there vis no interruption of the oscillations while the condenser is being charged in this form of Figs. 5 and 6, energy is transferred at the maximum rate above indicated, during the entire time as compared with the discharge interval only (out ofya much larger time taken for charge and discharge) in the process described bv me in connection With Figs. 1-4. By this method I estimate that for equal sources of power supply I can use condensers of about one-fifthk of the bulk or weightlthat I nd necessary to use with the form of my invention first described.

los'

These two advantages make it possible to greatly increase the. energy input with a y given bulk of condenser as compared with the energy input possible by means of my heating l It lends itself y first-described :form` and to supply the enorgy at a'high voltage which lsapplied to the circuit with or without intervening transformers according. to the voltage dcsired, obtaining large current How without appreciable reduction, in voltage.

It will be-evident that the oscillations produced by this second form of my invention are in a broad sense free oscillations, notwithstanding that they are maintained in amplitude and continuous in time, since their periods and maximum amplitudes are largely determined by the electrical constants of the condenser and inductor branches of the circuit and the frequency agreement with the supplly circuit, being the result or selection of t ese constants and not oi agreement forced by the dynamos or other source.

With the tuned circuit, having the ampli- -tude ot its oscillations maintained, thc intervals will depend upon the rate of changeoi' the electro-magnet impulses applied to the resistor which will depend upon the freuuency of the supply circuit, placing a premium upon high frequency supply.

` 7lfhe adaptation ci my second form tomilltiphese operation without unhalzrncinnJ the piensesl is lsuthciently'olovious not to require illustration'but does not oiier quite the saine advantage as in my first forni if a special generator he used; .This generator may be driven conveniently by a niultiphase induc- 'tion motor, peri'nittingsingle phase to he supplied hy the generator Without unbalancing..

My furnace is applicable to a great variety 'oi of a mass o metal or other material, in itself conducting, without regard to irregulerities in shape end perinittine' local application oi the heat to a particular belt or section or .even to aspot contiguous to the end of the coil upon the surface of a resistor as Awell as to crucibles, conducting or non-conducting, pr handling finely divided material or other material to 'be heated, melted o'rjsmelted.

particularly to crucible furnaces because t e resistor may be in a conipact mass` as no interthreading of magnetic culation. tubes are required. This permits convenient and effective heatingr invacuum' fitted with an air tight top 13 through which a tube 1-1 leads to a vacuum.. Within the container a crucible 115 is placed, supported heating applications including; the

furnaceshaving circuit interrupts its continuity and no cirupon sand or other filling 15 to bring it to the right height with respect to the coil, to suit the size of Crucible and the depth of content 16 in it. Either the crucible or the content may be the resistor.

The oscillation current, passed through the coil by reason of Whatever circuit connections, induces current {low-in the resistor in planes parallel to the planes of the coil. Skin eiiect causes the induced current to be somewhat more concentrated in an outer portion of the resistor than in other parts, heating the outer perimeter `n1ore rapidly than the inner portion and providing` a correspondingly large conduction area for transier oi heat to the inner part oi the reslstor. `Joule e'ect is also present. The dlrection of current dow in the oscillation coil is indicated by the outside -arrows -in Fig. 8, the inside arrows indicating the direction of induced current within the pool.

y proportioning` the cross section or a molten or otherwise liquidv resistor to the current the latter may be made `f ,great enough to develop pinch contraction of the current-carrying resistor giving1 effective stirring radially inward from the more highly heated outer part oi the pool. The direction oi the fluid new is modiiied by the Joule edect.' rll`he ei'ect o? this is shown by the circulation lines in Fig. 9, the directions of the impressed and induced current impulse being; shown hy the arrowpoints and teils in the circles lust outside and inside the Crucible walls. Thestirring is not oi the saine importance as the transfer of energy into heating oi the resistor, because of the ready conduction ci heat troni the outside inward. This is especially true since the crucihle content is the resistor end l deliver the heat directly within the mein body or M95 the molten or liquid mass, but where desired may be made proportionate to the need, to

maintain advantageous approach to uniformity of temperature;

It will be evident that each of the two forms illustrated possesses advantages ngt possessed by the other. The form shown- 1n Figs.l 1, 2, and 3 is capable of use with ex1sting commercial power circuits, whatever the frequency, with or` without transformer use according;r to the potential and w1thout une balancing multiphase circuits, and requires no extended outlay for apparatus other than the condensers and furnace. An eective and desirable inexpensive discharge gap for such use has been practically developed by me and is disclosed in .my application for patent for discharge gap, Serial No. 175,518, led June 18, 1917. Relative disadvantages exist in that. the -discharge takes place during a part only ofthe total time, inter` spersed between charging periods, and that t e amplitude of the oscillation is reduced les purpose desired by damping This requires that the bu or `u reight of condensers required is about ve times as at as torthe othercase oft sustained oscillations.

As the form shown in Figs. 5 and 6 re?.

of avoiding the necessityv for discharge gaps and of utilizing and maintaining continuous discharge having uniformly. high amplitude and a high eciency from a time standpoint i5 lbecause of its continuous operation. lt also obviates the need of a large bulk or Weight vof condensers.l y

Y ln either event the simplicity of the furnace, and its freedom from irregularities of shape and detached resistor partsl n iakes it approach the ideal furnace, particularly when applied to crucible work in melting,

reiining or heat-treatment of materials.

The crucible form is easy to fill and c mpty and the content can be chilled and again relieated without breakage of the Crucible.

rlhc resistor is heated as a mass and isv less dependent upon circulation for the heating than in other inductive forms free from contamination by gases. Commercial freiuencies'of supply can be used with one o the forms illustrated and without unbalancing polyphase circuits. Since the material heated is in a mass of approximately cylinvolume is small and this greatly reduces heat losses. The wer factor may be maintained substantia ly at imity .and the elliciency reactance and in which the normally low wer factor otherwise resulting from the positive reactaiice is corrected by capacity thrown across the positive reactance or acrossthe generator terminals (with proper 'connections' these would be substantially e0 equivalent) with the effect of balancing the positive reactance by the negative` reactance of the capacity until unity power factor is secured in'tlie supply circ has been such an approach drical form, the ratio of .radiating surface to cillating with decreasing amp second forni, is intended by me to t, or until there thereto for the that further perfection of incassa 452 amperes in the furnace coil circuit, provided the capacity shunting the generatorterminals is one niicrofarad and the induc` S0 tance of the furnace coil is properly chosen se that the power factor for thegenerator circuit 1s unit-y.

lf the furnace is absorbing no power, then.

the current supplied by the generator is negligibly Small, While the current through the furnace inductor coil remains substanlt-ially the saine, the current in the' inductor coil and the current flowing through. the

condenser being in this case different lin phase by almost exactly 180 anditherefore almost-Wholly wattless.

I. As the demand from the furnace increases, this angle of nearly 180 is reduced and the proportion of watt currentto watt- 9.54 l less current in the furnace inductor coil increased with corresponding greater demand upon the generator and larger current sup ply from it.

`'lhe impulses given by thhitwo types of 10o current which I prefer to usci` (the one ositude as it is 'damped and the other oscillating with the same amplitude, maintained 'by reason of the energy continuously supplied to it) have both been called by me free oscillations and oscillatory. These terms are intended to distinguish them. from the forced oscillations delivered by an alternating current generator in some of my claims, as I intendv not to cover such alternating'current also.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is 1. An inductor heating coil adapted to heating a resistor and freefrom complete or partial interlinkage 0f transformer iron with the resistor in combination with high frequency 4current supply for the coil.

2. A non'- magnetic mass to be highly 120 heated, an induction coil in operative relationthereto and a high frequency current supply for the induction coil.

3. In a heating system a hollow induction coil adapted to heating a resistor and means for passing high frequency current throughthe coil.

4. In a heating system a hollow heating coil adapted to heating a resistor and free from partial or complete .transformer inag- 130 'insane netic interlinkage therewith lin combination with means for Ypassing highrequency curl rent through the coil.

. 5. ,A heating system havin inductive transfer of electric energy at hig frequency from the inductor element to the resistor, transformed into heat therein andfree from transformer iron.

6. Induction heating mechanism comprising a hollow conducting coil providing a vspace within for a resistor ada ted to re-v ceive succeive materials to be -cated and. a. source of high frequency current supply for said coil. y

'7. Mechanism for inductively` treating a resistor, comprising a'conducting coil, material to be treated in inductive relation thereto, a condenser, a lcharging; source of current for said condenser and connections for discharging the condenser through the 1 coil.

8. In aheatin device, a container for a liquid pool, acon ucting coil adapted to surround said pool, a condenser connected to 'other the 'two parts of tliedivided circuit forming a circuit -in approximate' tune with the source of supply and free fromdischarge gap interruption.' l

15. A high frequency high tensionA alternoting current source of supply, 'a heating coil providing inductance und adapted to discharge through said coil and means for successively charging'and discharging said condenser. -V

9. In a heating device, an electrically conducting coil, an electrically non-conductin container therein ada ted to hold materia in molten ore liquid orm and free oscillation current supply for said coil.

10. In a furnace, anfalternating source of current supplyV of high' frequency and branched 'circuits to which it is connected, having res ectively capacity and a heatin coil provi ing inductance, thev capacity an l inductance being proportioned to form a Icircuit.

cuit of the branches approximatel7 resonant with the alternating current supp y.

11. In a furnace, an alternating current .source-of supply and a divided circuit to which it is connected and in approximate resonance .with the supply andhaving a furtially a negative reactance.

18. An electric heating device whose circuit contains a nega-tive reactance, in combination with supply current therefor having a positive l reactance.

19. A high frequency current electric furnace having a secondary charging circuit "provided with anegative reactance.

20. A furnace, an oscillation discharge electromagnetic induction, to

circuit therefor, includinga condenser and a high tension. chargingcircuit" therefor which, with the condenser, tends to lgive a leadinL 21. cuit naturally has a negative reactance in combination with positive 'reactance comcurrent. v

ensating therefor to produce unity power.

actor in the supply circuit..

22. The -inethod of applyiii energy vby' ge converted into heat within a removable resistor mass,

which consists in passing high frequency ,currents about the resistor free from internace coil in one branch of the divided cir- 12. In a heating device a high frequency -alternatingcurrent source of supply and a Adividedjcircuit connected therewith having capacityjandA inductance in its respective branches proportioned to bring it into approximate tune with the source of supp y i nating en d including in the inductance a heating coi ' 18. A heating coil providin inductance,

' a condenser in circuit therewit. and a high voltagel alternating current source of su ply to which the circuit is approximate y tuned and connected with the circuit across the condenser terminals.y

14. A high frequency high tension. altera divided circuit to -which it is a p ie having a furnace coil providing in uctance in one part of the circuit and a capacity in the linkage vof a transformer 'magnetic circuit with the electric circuit. l y

23. .The method of applying energy by electromagnetic induction to be converted n electric heating device whose cirinto heat within a resistor mass which consists in passing high frequency lcurrent through a conducting coil surrounding the resistor to be heated. y 24. The method of transferring electric energy into a mass so as to become thermal ener therein by electromagnetic induction whic consists in circulating high frequency currents in inductive relation to the mass,

free. from interlinkage of a. transformer.Y

magnetic circuit with the electric circuit.

2 5. The method of furnace heating which consists 'in inducing electric current ilow 4 current source of electric suppl and within thel pool directly from electric current flowoutside the pool, as distinguivlied from linking thematerial in thepooland the outside current by a transformer magnetic circuit.- n

26. The method of heating electrically hof conducting substances not capablef of eii'ec-a `tual magnetization which consists in induc- ,ing electric currents therein from a current carrying coil directly, without inter-position of a transformer magnetic circuit.

'27. The method of heating a. poohywhich v consists in utilizing the body of the pool as a secondary for a. high vreqiiency current primary.

,28. Tliemethod of heating material. in liquid condition which consists in'discharging-a condenser through a\coil surrounding the material.

29. The methodof heating molten metal which consists in setting up closed-circuits .of electriccurrent flow inthe metal having periodlike tliatof free oscillation'currents.

30. The' method 'of heating molten metal i whichfconsists in'placing the metal in a sequent upward'movement of the center of -the pool and downward movement oftheA material inproximity to its circumference. 32. The method of stirring molten metal which consists in placing a conductingcoil u in inductive relation to the metal and trans- I which consists in electrcally forcing molten. metal from'tlie out'er part of said pool be pool-'to take the .50y f about the circumference of )i to produce electroma etic circulation from.'

ittingtihilpufgh. said coil electric current avinh g requenc1es.

4- 33. e nethod` of stirring a liquid pool by electromagnetic action which consists in ,setting up in it currents in closed circuitsvhaving thei-same 'periodicity as free osciltlatory currents. A 34. .The method of stirring a molten pool tween the topV andthe bottom inwardly in 'substantially radial' lanes with resultant-l .ow of metal from t e otheriparts of the place of `the molten metal displaced.' 5

method of-stirring a furnace re'- sistor which consists'in' circulating currents molten resistor thev more hl eated circumference 'toward the middei4v 51sV i which consistsin circulating high 'frequency "36. Themethod ofstirring a' furnace po'ol current through it near its-v rimetei".

37.The method of stirring a mass of 'electric conducting molten or otherwise- `liquid'material which consists in inducing flow ofhigh frequency current'through it in closed substantially horizontal crcumferen ltial paths near itsv perimeter. Vl-38. lflie'method f obtaining unity-power .'factor 'inan' electric .heating circuit -con-v difference.

tremitics' of the con ensei', so vp with such circuit constants as to approxi-Y nected'with a vsupply having a positive reactancewhich- `consists/in providing more thanenough negativeJ reactance in the heating circuit.to-overcomethe positive reactance of the supply and balancing thetwo by a negative reactance to take a leading current and balancing `the .two reactances against each other to improve the power factor.

, 40. rlhe method of improving the power factorin electric furnace operation which cnsists in connecting a furnace having negative reactance in its circuit with a current supply having positive reactance and balancing' the reactances to produce unity power factor by .introducing a reactance substantially equal tothe difference 'of the reactances of. thev furnace and snpplyand.

having an opposite sign from that of their 414. The method -of applying energy by electromagnetic induction 'to be converted into heat within a resistor mass, which consists in passing -liigh frequency oscillation currents about the resistor; and Vmain the amplitude of the oscillations. Y

` 42.. The' method '0f\ applying energy by electromagnetic induction to he' converted into heat within a resistor mass, which consists in supplying high frequency current 'to a circuiti in ap roximatetune therewith containing aheating coiland containing also I ercby passing current of thesame frequency through the-coil to inductively heatthe resistor.

a condenser and th 43. The method of inductiveiy transftr- -ring energy from ,a coil to a i-csistor` to be a circuit with a, condenser, the being free f roin discharg'egap interruption, and apply mg to the circuit at two mts at opposite exand matelyv tunel the condenser-coil circuit 44. The method of forming powerful inductive heating ciments wlnc consists in dischar currents from a condenser through a hea Y coil and maintaining the: amplitude of discharge and at the sama time supplying energy to e circuit by an outside electric circuit'with which the cir- 'cuit through the coil is in approximate. tune.

45. The method' of. increasing theeiciency of oscillation current discharge for electric heating which consists .ii providing 4high frequency valternating current supply forthc heating circuit and at the saine time 'main-- taining the-'amplitude of the oscillations witiiili the iso frequency alternating current and applying i heated which consists in placing the coil in vio impec v the oscillations oontinuous by IPPNXIDIWLY heating circuit and fin lsupp energy Aof i frethrough v'thereto from an outside source gh quency alternating current at opposite terminals of the inductor. 4:7. The method of obtaining high current" values out ofphase with the electromotive force in a heating circuit while maintaining the current in the supply circuit in approximate phase with its electromotive force which consists in forming the heating circuit as a divided circuit containing in uctance within the-heat' coil .zand also a condenser and in applyingmigh frequency alternating 20v currentsupply across the condenser.

48. The method of correcting the phase reff llation between-the electromotive forceand current in a generator circuit feeding c urrent through a furnace inductor coil` having a positive reactance which consists in utiliz-V ing a bridging negativereactance to coni .risate for the positive reactance of the in uctor coil and to-secure unity power factor.

49. The method of securing a high current a furnace, inductor circuit with low current and high 'power factor in an alter.- nating current supply circuit therefor,vwhich consists in placing the inductor'furnace coil in one branch of a divided circuit fed by the su pl .circuit and including capacity in the 36 ot er ranch thereof, where -y t e current in the divided circuit is displaced with respect toits electromotive force tovarying d depending upon the energy consumed in the furnace coil and approaching 180 as the 4o energy consumed therebraiproaches zero.

EDWIN v l ORTHRUP.

Witness:

J. Lumnau Kaorrims. 

